javaScript的Date函数

1、获取当前时间

　　Date()获取到的时间是当前设备的显示的时间，开发中要考虑到用户的设备时间是否正确

let nowTime = new Date(); // 获取当前时间

　　把data时间转换成常规格式

<script>
            let getTimeNow = () => {
                let nowTime = new Date(); // 获取当前时间——Sun Jan 12 2020 14:07:22 GMT+0800 (中国标准时间)
                let year = nowTime.getFullYear(); // 年
                let month = nowTime.getMonth()+1; // 月 这里要加1
                let day = nowTime.getDate(); // 获取几号
                let hour = nowTime.getHours();//得到小时
                let minu = nowTime.getMinutes();//得到分钟
                let sec = nowTime.getSeconds();//得到秒
                let week = nowTime.getDay();//得到星期几
                let timeStr = '';
                timeStr += year + '/' + isGreaterthanTen(month) + '/' + isGreaterthanTen(day); 
                timeStr += '-' + isGreaterthanTen(hour) + '/' + isGreaterthanTen(minu) + '/' + isGreaterthanTen(sec);
                timeStr += '-' + getWeek(week);
                return timeStr;
            };
            let isGreaterthanTen = num => {
                if (parseInt(num, 10) >= 10) {
                    return num;
                } else {
                    return '0' + num;
                }
            };
            let getWeek = week => {
                if (parseInt(week, 10) === 0) {
                    return '星期日'
                } else if (parseInt(week, 10) === 1) {
                    return '星期一'
                } else if (parseInt(week, 10) === 2) {
                    return '星期二'
                } else if (parseInt(week, 10) === 3) {
                    return '星期三'
                } else if (parseInt(week, 10) === 4) {
                    return '星期四'
                } else if (parseInt(week, 10) === 5) {
                    return '星期五'
                } else {
                    return '星期六'
                }
            };
            console.log(getTimeNow()); // 2020/01/12-14/25/29-星期日
        </script>

2、时间戳

 　　获取当前时间戳：

　　　　　　　// 获取当前时间戳
            let timestamp1 = Date.parse(new Date()); // 精确到秒
            let timestamp2 = (new Date()).valueOf(); // 精确到毫秒
            let timestamp3 = new Date().getTime(); // 精确到毫秒
            let timestamp4 = Number(new Date()) ; // 精确到毫秒
            let timestamp5 = Date.now(); // 精确到毫秒   

　　把时间转换成时间戳

<script>
            let getTimeNow = (nowTime) => {
                // let nowTime = new Date(); // 获取当前时间——Sun Jan 12 2020 14:07:22 GMT+0800 (中国标准时间)
                let year = nowTime.getFullYear(); // 年
                let month = nowTime.getMonth()+1; // 月 这里要加1
                let day = nowTime.getDate(); // 获取几号
                let hour = nowTime.getHours();//得到小时
                let minu = nowTime.getMinutes();//得到分钟
                let sec = nowTime.getSeconds();//得到秒
                let week = nowTime.getDay();//得到星期几
                let timeStr = '';
                timeStr += year + '/' + isGreaterthanTen(month) + '/' + isGreaterthanTen(day); 
                timeStr += '-' + isGreaterthanTen(hour) + '/' + isGreaterthanTen(minu) + '/' + isGreaterthanTen(sec);
                timeStr += '-' + getWeek(week);
                return timeStr;
            };
            let isGreaterthanTen = num => {
                if (parseInt(num, 10) >= 10) {
                    return num;
                } else {
                    return '0' + num;
                }
            };
            let getWeek = week => {
                if (parseInt(week, 10) === 0) {
                    return '星期日'
                } else if (parseInt(week, 10) === 1) {
                    return '星期一'
                } else if (parseInt(week, 10) === 2) {
                    return '星期二'
                } else if (parseInt(week, 10) === 3) {
                    return '星期三'
                } else if (parseInt(week, 10) === 4) {
                    return '星期四'
                } else if (parseInt(week, 10) === 5) {
                    return '星期五'
                } else {
                    return '星期六'
                }
            };
            // 获取当前时间戳
            let timestamp1 = Date.parse(new Date()); // 精确到秒
            let timestamp2 = (new Date()).valueOf(); // 精确到毫秒
            let timestamp3 = new Date().getTime(); // 精确到毫秒
            let timestamp4 = Number(new Date()) ; // 精确到毫秒
            let timestamp5 = Date.now(); // 精确到毫秒   
            
            let timeStr = new Date(1578811134211); // 放入时间戳
            console.log(getTimeNow(timeStr)); // 2020/01/12-14/38/54-星期日
            console.log(timeStr.toLocaleDateString().replace(///g, "-") + " " + timeStr.toTimeString().substr(0, 8)); //再利用拼接正则等手段转化为yyyy-MM-dd hh:mm:ss 格式
        </script>

3、倒计时

　　计算时间戳

<script>            
            let timeEnd = 1578987896323; // 结束时间的时间戳 
            
            let countDown = (timeEnd) => {
                let timeNow = new Date().getTime(); // 当前时间戳
                let remainingTime = parseInt(timeEnd) - parseInt(timeNow);
                secondTime(remainingTime);
            };
            let isGreaterthanTen = num => {
                if (parseInt(num, 10) >= 10) {
                    return num;
                } else {
                    return '0' + num;
                }
            };
            
            let secondTime = (remainingTime) => {
                /*
                 1 秒 s = 1000 毫秒 ms
                 1 分 min = 60 秒 s
                 1 时 hour = 60分 min
                 1 天 day = 24 小时 hour
                 1天等于 86400000毫秒(ms)
                 * */
                let timeStr = '';
                let days = Math.floor(remainingTime/(24*3600*1000)); // 相差天数
                if (days > 0) {
                    timeStr += isGreaterthanTen(days) + '天';
                } else {
                    timeStr += '00天'
                }
                
                let hoursLeave = remainingTime%(24*3600*1000)    //计算天数后剩余的毫秒数
                let hours = Math.floor(hoursLeave/(3600*1000));  // 相差小时数
                if (hours > 0) {
                    timeStr += isGreaterthanTen(hours) + '时';
                } else {
                    timeStr += '00时';
                } 
                
                let minLeave = hoursLeave%(3600*1000);        //计算小时数后剩余的毫秒数
                let minutes = Math.floor(minLeave/(60*1000));
                if (minutes > 0) {
                    timeStr += isGreaterthanTen(minutes) + '分';
                } else {
                    timeStr += '00分';
                }
                
                let secounLeave =minLeave%(60*1000);      //计算分钟数后剩余的毫秒数
                let seconds=Math.round(secounLeave/1000);
                if (seconds > 0) {
                    timeStr += isGreaterthanTen(seconds) + '秒'
                } else {
                    timeStr += '00秒';
                }
                return timeStr;
            }
            console.log(countDown(timeEnd));
        </script>

　　4、yyyy-MM-dd HH:mm:ss 转换成时间戳

            // 获取某个时间格式的时间戳
            let stringTime = "2020-01-01 00:00:00";
            let timestamp = (new Date(stringTime)).getTime();
            console.log(timestamp);